Interpretive Summary: Male beetles known as cowpea weevils (Callosobruchus maculatus), were allowed to fly upwind to sex pheromone collected from female cowpea weevils. The flight patterns/tracks of these males were video recorded as they flew upwind at three wind speeds. The flight tracks were analyzed for the beetles' modifications of their flight speeds and steering in response to the different wind speeds. These male beetles maintained nearly identical ground speeds at all three wind speeds, consequently their airspeeds were higher at the higher wind speeds; to accomplish this the beetles steered more directly upwind at the higher wind speeds. The male beetles, like extensively studied male moths, flew in generally zigzag patterns across the upwind line and did so at the same regular tempo (approx. 3.4 turns/sec) in all three wind speeds. This is the first such study on free-flying male beetles; other beetle species in our lab appear to fly similarly, but it is not yet clear whether they respond to plume structures and changes in stimulus strength in manners similar to male moths.

Technical Abstract:
Two-day-old male cowpea weevils, Callosobruchus maculatus, were released individually and flew upwind to a point source of female sex pheromone at three wind speeds. All beetles initiating flight along the pheromone plumes made contact with the pheromone source. Analysis of digitized flight tracks indicated that C. maculatus males responded like moths tested under similar conditions. Net and actual ground speeds remained constant, whereas airspeeds increased with increasing wind speed. Beetles adjusted their course angles to fly more directly upwind in higher wind speeds whereas track angles were constant at each wind speed. Cross-wind traverses were generally narrow and were not different at the wind speeds employed. The tempo of these counterturns across the wind line was nearly constant regardless of wind speed, and there was little variation among individuals. The main contrast to moths' zigzagging flight was the generally straighter upwind flight by these beetles. Male moths typically produce a bimodal distribution of track angles to the left and right of the windline, whereas C. maculatus males' track angles were unimodal about 0°. This is the first detailed flight track analysis of a beetle species. Other beetle species in our lab appear to fly similarly, but it is not yet clear whether they respond to plume structures and changes in stimulus strength in manners similar to male moths.